Metal paste pigment



Patented Oct. 31, 1939 UNITED, STATES arzarw METAL PASTE mama Edwin L. McMahan, New Remington, 2a., alsignor to Aluminum Company of America, Pittsburgh. Pa., a corporation of Pennsylvania No Drawing. Application November 11, 1987,

.. Serial No. new j This invention relates to improvements in the production of metal. paste pigments, and more particularly to the production of aluminum paste pigments having improved stability of leafing g power.

' The metal paste pigments are generally prepared by subjecting the desired metal to a preliminary comminutlng process to reduce it to a convenient, relatively large particle size.. The

1o comminuted metal particles are then placed in a ball mill or equivalent device, together with a liquid thinner, preferably mineral spirits, and a leafing agent such as stearic acid and/or pahnitic acid. The ball mill is then operated until the 16 repeated impact of the steel balls therein has reduced the metal charge to a sludge containing the metal pigment in very thin flake-like particles coated with the stearic acid or other leafing agent used. This sludge is removed from the 9 ball mill and any excess of the liquid phase or thinner is removed, generally by filtration. By removal of this excess liquid it is possible 'to eliminate certain dark-colored colloidal particles formed during the milling operation which, if

as not removed, might detract from the value of the paste as a pigment. It ispossible in this operation, if desired, to adjust the final product to the exact consistency preferred for the metal paste pigment for marketing. In practice, how- 80 ever, the thinner is generally removed until the residue constitutes a substantially dry filter cake which contains about 80% or more of the metal, the balance being retained thinner and leafing agent. The filter cake so produced is then gen- 35 erally adjusted to a metal content of aboutp60 to 70%, depending upon the use to which the dual product is to be subjected, by the addition of a predetermined amount of fresh thinner liquid to 5g ment is mixed with a satisfactory paint vehicle it will be observed that a continuous layer of the metal pigment forms on the surface of the vehicle when stirring is stopped. This phenomenon is known as leafing and imparts to metal 55 pigment paint coatings smoothness, brightness and other desirable properties. The phenomenon of leafing is apparently one of surface tension directly attributable to the thin film of leafing agent formed on the surface of the indi V vldual metal flakes.

In the case of a metal powder pigment, such as-an aluminum powder pigment, formed in a stamp mill, leaflng power is generally imparted tothe powder by the film of polishing agent applied to the surface of the metal particles in the i0 polishing step of the process. On the other hand, in the case of a metal paste pigment, such as an aluminum paste pigment, the film is formed by specific agents added to the ball mill charge for the purpose of imparting leafing power to the metal particles, which agents are known in the art as leafing agents. These .leafing agents are generally selected from the group of fatty acids, such as stearicacid, palmltic acid, or mixtures of these acids. The leafing agent is proba- 20 bly preferentially organized or molecularly oriented on the surface of the metal particles in some manner which promotes the leafing action. Alteration of this organized film either by chemical or physical action may result in loss of leafing power. For example, by simply heating an aluminum paste pigment in an oxygen-containing atmosphere to a temperature above about 50 C. the leafing power of the pigment may be substantially impaired. While it has been recognized that the leafin power of aluminumpowder may increase as a result of the aging process after the polishing operation, probably because preferred orientation of the molecules is taking place, it has been found that, with the exception of a brief period immediately following its formation, there is a tendency for an aluminum paste pigment to lose leafing power on agirg. This is particularly true on long continued storage or storage at elevated temperatures or in the presence of moisture. This loss of leafing power in aluminum paste pigments is probably due to some'modificationof the film of leafing agent during the aging period. v

It is an object of this invention to provide a stabilized metal paste pigment having improved persistence of leafing power.

It is more particularly an object of thisinvene tion to provide a stabilized aluminum paste pigs. ment having improved persistence of leafing power. v This invention has as a further object the provision of a process for the production of metal paste pigments in which the ability of the metal pigment to leaf is substantially stabilised.

A further object of this invention is to-aiford a relatively simple method for increasing the persistence of leafing power of aluminum paste pigments by producing on the aluminum particles contained therein a substantially stable film of leafing agent.

I have found that by the addition to the leafing agent and thinner .used in the production of metal paste pigments of certain organic aromatic chemical compounds, the film of leafing agent formed upon the metal fiakes can be stabilized and the leafing power of the resulting paste improved so that it is maintained even under adverse conditions of storage to which the paste may be subjected. The compounds which I have found to be suitable stabilizing compounds for the purpose of my invention are compounds selected from the group consisting of thephenols and the amino phenols, such as phenol, monobenzyl amino phenol, p-tertiary amyl phenol, guaiaphene (a' mixture of phenols'from wood distillation), and the like, or mixtures thereof.

'The amount of any one of these substances required to stabilize and substantially increase the persistence of leafing power of a metal paste pig- .ment will vary with the particular substance used and with the amount of leafing asent present in the paste. In any case, the amount of stabilizing compound required is relatively-small, and I have found that in most cases, by the addition of the stabilizing compounds in amounts on the order of about 0.002 to 0.1% of the finished paste, satisfactory results can be obtained.

When using phenol, p-tertiary amyl phenol or guaiaphene, I have found it generally preferable to use these compounds in somewhat greater amounts than when monobenzyi amino phenol is used. I prefer, for example, to use phenol. p-tertiary amyl phenol or guaiaphene in 'an amount corresponding to about 0.05% by weight of an aluminum paste pigment containing approximately 1% of stearic acid as a lemng agent, while the preferred amount of monobenzyl amino phenol for use with a similar paste is about 0.005% by weight of the paste.

Although these phenolic stabilizing substances are not in themselves considered to be leafing agents, I have found that a small amount of these stabilizing compounds can be used to replace a bilizing compounds of my invention in somewhat greater amounts than 0.1%. Thus, for eroample, it maybe desirable to replace a substantial part of the leafing agent with a stabilizing compound where a relatively large amount of leafingagentinthepastemaybeundesirable v because of a low solubility in the mineral spirits thinneror for other reasons. For example, I. have been able to produce satisfactory aluminum paste pigments at relatively low cost where as much as one-half of the usual amount of leafing asent was replaced with a small amount of stabilizing compound. I have obtained satisfactory results by replacement of substantial proportions ofthe leafing agent with as little as 3&0 oftheweightofsaidportionofoneormoreof the phenolic stabilising compounds of my invention Instabiliaingtheleafingpowerofmetalpaste pigments made by the ball mill process. such as those referred to above, the phenolic compounds of my invention may be incorporated at any convenient point of the process. It is preferred'to incorporate the stabilizing sub- I stances in the fresh thinner solution, with or without additional leafing agent employed to adjust the metal content of the substantially dry filter cake obtained after, the filtration step. Satisfactory results have been obtained, however, when the stabilizing compoimd is incorporated as part of the charge in theball mill and when so added it functions to protect stabiliaethefilmofleafing agentfromthe of application of the leafing agent to the metal 1g flakes.-Goodresults have likewise been tained by the addition of the stabilising cempoundbothtothechargeintheballmiliand the'filter cakeusedinmakinguptheilnished I The following comparative tests will serve to illustrate the desirable results obtainable by the use of phenolic leafing power stabilising compounds according to my invention. The comminutedaluminumwasplacedinaballmillwith I 'amineralspiritsthinnerandstearlcacid. It was reduced to a sludge containing flaked aluminum. The excess thinner was fitered from this sludge to produce a filter cake containim about 82% of aluminum flakes. about 1% of 8 stearic acid, and about 17% of mineral spirits. To a 200-gram portion of this aluminum pigment filter cake there were added 54 grams" of a solution of mineralspirits containing 1.35 grams of stearic acid and-0.135 gram of phenol, and the whole mess was'thoroughly mixed to form the finished paste. For comparison, to another 200- gram portion of the hluminum pigmentfilter cake there were added 54 grams of a solution of mineral spirits containing 1.35 grams of stearic acid and no phenol, and the whole mass was thoroughly mixed to form the finished paste. These two test portions were then subjected to identical test conditions to determine the relative stability of their leafing power. They were stored in containers at a constant temperature of 40 C. and in an atmosphere saturated with water vapor. These conditions represented highly abnormal storage conditions and provided an accelerated test of the relative persistence of leafing power of the two samples. The leafing power of each of the-two samples was determined periodically throughout .the test. 'Ihe methodused for determination of the leafing powerwas the standard spatula leafing test dell scribed in Aluminum Paint and Powder", by J. D. Edwards, published in 1938 by Reinhold Publishing Corporation. After five days of exposure to these accelerated test conditions the sample containing no phenol showed a substan- O tially complete loss of leafing power, whereas the sample containing phenol still retained satisfactory leafing power.

'States Patent, Serial No. 174,061, filed Novemher. 11", 1937, there is described and claimed the 15 use of aniline and paraphenylene diamine and pigment, selectediromthe group consisting of 'monoamyi amine, diamyl amine, triamyl amine, at least one compound capable of stabilizing production of metal paste pigments having imthe group consisting of phenol monobenzsl vtaming a fatty acid leaflng agent at least one 8. A stabilized aluminum paste pigment havan aluminum paste pigment containingstearic bensyl amino phenol, p-tertiary amyl phenol, acid, 0.002.to 0.1% or at least one compound and guaisphene.

the like as stabilizing compounds for the produc phenol, monobenzyl amino phenol, p-tertiary tion or metal paste pigments having improved .amyl phenol, and guaiaphene. persistence of leailng power. In my copending 5. A method for the production of aluminum application for United States patent, Serial No; paste pigment having improved persistence of 5 1%,062, flied November 11, l93'1,'there is deleaflng power. which comprises incorporating in scribed and claimed the use of amines. such as an aluminum paste pigment containing stearic alpha naphthyl ,amine, beta naphthyl amine, acid and a mineral spirits thinner, 0.002 to 0.1%

and the like as stabilizing compounds for the the leaiing power of the pigment, selected irom proved persistence of leaflng power. amino phenol, p-tertiary amyl phenol, and guai- I claim: v aphene. Y 1. A methodior the production of metal paste 6. A sta ilized metal paste pigment having impigments having improved persistence of leaflng proved persistence of leafing power, comprising power, which comprises incorporating in said metal flakes, a leaflng agent, and a compound paste pigment at least onev compound, capable selected from the group consisting of phenol, ofstabilizing the leaflng power of the pigment, monohenzyl amino phenol, p-tertlary amyl pheselected from the group consisting of phenol, nol, and guaiaphene.

monobenzyl amino phenol, p-tertiary amyl phe-' '7'. Astabilized aluminum paste pigment havgo nol, and guaiaphene. ing improved persistence of leafing power, com- 2. A method for the production of 'an alu- 'prisingaluminum flakes, a leaflng agent, and a minum paste pigment having improved percompound selected from the group consisting of sistence of leaiing power, which comprises in- /phenol, monobenzyl' amino phenol, p-tertiary corporating in an aluminum paste pigment conamyl phenol, and guaiaphene.

compound, capable of stabilizing the ,leaflng ing improved persistence of leaflng power, compower of the pigment, selected from the group prising aluminum flakes, stearic acid, and a comco'nsistlng of phenol, monobenzyl amino phenol, pound selected from the group consisting of phep-tertiary amyl phenol, and guaiaphene. nol, monobenzyl amino phenol, p-tertiary amyl 3o 3. A method for the production of aluminum phenol, and guaiaphene.

paste pigment having improved persistence of 9. A stabilised aluminum paste pigment havleaflng power, which comprises incorporating in ing improved persistence of leaflng power, coman aluminum paste pigment containing stearic prising aluminum flakes, stearic acid, mineral acid at least one compound, capable of 'stabilspirits, and a compound selected from the group izing the leafing power of the pigment, selected consisting of phenol, monobenzyl amino phenol, from the group consisting of phenol, monobensyl p-tertiary amyl phenol, and guaiaphene.

amino phenol, p-tertiary amyl phenol, and guai 10. A stabilized aluminum paste pigment havaphene. p a a ing improved persistence oileaflng power, com- 4. A method for the production of aluminum prising. aluminum flakes, stearic acid, mineral 40 paste pigment having-improved ersistence of spirits, and 0.002 to 0.1% or a compound selected leaflng power, which comprises incorporating from the group consisting of phenol, monocapableoistahililingthclsaflnlpovcroithe 

